Refractive laser surgery can be of tremendous visual benefit for patients. There is hardly any procedure in medicine as gratifying for a physician and patient as improving vision without the aid of an artificial device. Laser refractive surgery when properly performed on a suitable candidate is generally safe and effective. However, complications from laser refractive surgery can be difficult, if not impossible, to remedy or alleviate. Significant complications from lasik or PRK often lead to litigation. In such cases expert witness testimony for refractive laser surgery may be helpful.
Refractive Laser Surgery to correct myopia, hyperopia, and astigmatism is subdivided into three major types:
- Lasik (Laser-assisted in situ keratemileusis). Unlike other forms of laser refractive surgery, lasik involves the production of a thin “porthole” flap of cornea that is retracted during the procedure. The thin flap is produced by either cutting with a blade or by laser (intralasik). Excimer laser treatment is applied to the bed of underlying cornea to reshape the eye. The thin flap of tissue is then placed back in position. The advantage of lasik with a flap is quicker healing and less discomfort than other types of laser refractive procedures.
- Lasek (Laser-assisted subepithelial keratemileusis). In this type of laser refractive surgery, a thin flap is peeled away from the surface. This flap is thinner than that performed by regular lasik.
- Photorefractive Keratatectomy (PRK). The superficial surface of the cornea is removed and excimer laser treatment applied directly on the cornea.
In each form of refractive laser surgery the shape of the front window of the eye (cornea) is modified to focus light rays more precisely on the retina. Vision is maximized when the greatest numbers of light rays are properly focused on the retina. The retina, like the film in a camera, translates the light rays to electrical impulses that are relayed to the brain through the optic nerve.
Examination for Candidacy
One of the important parameters of determining candidacy involves measurements of the cornea. Patients wearing contact lenses are instructed to suspend wearing contact lenses because contact lenses may change the shape of the cornea and alter readings of the cornea in its natural state. Patients who wear hard contact lenses are often instructed to suspend contact lens wear for a prolonged period of time.
Refraction is the measurement of the degree of nearsightedness (myopia), farsightedness (hyperopia), or astigmatism (irregularity). A refraction may be performed by a machine (automated refractor), by subjective testing (manifest refraction), or by the use of eyedrops that relax the eye muscles to give an assessment of the natural state of the eye without muscle influence (cycloplegic examination).
Anterior Segment examination is an assessment of the front portion of the eye to determine the presence or absence of pathologic conditions that may influence the outcome of refractive laser surgery.
Posterior segment examination is an assessment of the back portion of the eye to determine the presence or absence of pathologic conditions that may influence the outcome of the refractive laser surgery.
Corneal Measurements
- Pachymeter
This instrument measures the thickness of the cornea. - Topography
This instrument measures the contour of the eye. The front window of the eye (cornea) has microscopic irregularities, and this instrument maps the peaks and valleys. Advanced topographic machines map the paeks and valleys of the front and back of the cornea.
Expert witness testimony may address these complications of laser refractive surgery
- Ectasia
While rare, ectasia is one of the more severe complications associated with laser refractive surgery. In this situation, the cornea is thinned to the point where it begins to bubble inwards or outwards. This type of complication is more commonly associated with laser refractive procedures that involve the production of a corneal flap and laser treatment for high levels of myopia or farsightedness. One of the original principles of laser refractive surgery is that at least 250 microns of corneal tissue must remain after the creation of a flap and removal of corneal tissue by application of excimer laser. However, this guideline is subject to the influence of other corneal parameters. Ectasia may lead to a pronounced irregular corneal shape that distorts vision, a condition known as keratoconus. A predilection for corneal ectasia may often be detected on topographic maps of the cornea. - Buttonhole flaps
This is a complication that happens during the procedure. As the corneal flap is created in lasik, the blade or laser may cut too thin in the central area of the flap. As a result, a slit opening (buttonhole) is inadvertently created in the corneal flap. The lasik procedure is usually aborted when a buttonhole occurs and the cornea allowed to heal for several months before attempting another lasik procedure. - Epithelial ingrowth
Superficial cells on the surface of the cornea may grow underneath the flap. When this happens the cornea can become hazy and irregular, compromising visual clarity. The corneal flap may need to be relifted and the cells growing underneath the flap removed. - Flap striae
The flap may not settle evenly on the corneal surface. When this occurs, folds known a striae may develop to cloud or distort vision. The corneal flap may need to be relifted and positioned properly before the striae become permanent. - Dry eye syndrome
Corneal nerves responsible for regulating tear flow are affected in refractive laser surgery. The amount of dryness may be assessed preoperatively by clinical observation and tear testing. There seems to be a direct correlation between the amount of laser refraction and the degree of dry eyes. Many patients undergoing lasik will have dry eyes for a few months prior to lasik.
Cases in Point
Dr. Reynard was retained to evaluate visual impairment in a patient with a history of dry eye syndrome exacerbated by lasik surgery.
Dr. Reynard was retained to evaluate cases of refractive laser surgery to determine adequacy for meeting the standard of care regarding pre-operative evaluation and performance of lasik surgery.
Dr. Reynard was retained to evaluate pre-operative topographic corneal maps in a patient who developed corneal ectasia after lasik surgery.
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